Opioids are highly effective as analgesics and are commonly prescribed for the treatment of acute and chronic pain. They are also commonly used as antitussives. The opioids, however, also produce euphoria and/or “drug liking effects” and are highly addictive. As a result they are often abused with far reaching social and health related consequences.
Because of the inherent potential for abuse, it is desirable that any pharmaceutical composition containing an opioid agonist be made as abuse-resistant or abuse-deterrent as practical. Illicit users often will attempt to insufflate, inject or otherwise misuse the product in order to achieve a more efficient or immediate effect from the opioid agonist.
Despite their addictive properties and the potential for abuse, morphine-like drugs, particularly, codeine, hydrocodone, hydromorphone and oxycodone have been routinely prescribed as treatment for severe, acute and chronic pain for decades. This is, in part, because there are currently no better alternatives to relieve severe pain that is resistant to other less potent analgesics such as non-steroidal anti-inflammatory drugs (NSAIDS). In this regard, there is a need to decrease the abuse potential of opioid analgesics. Thus far, approaches taken, unfortunately, have not solved the problem.
Hydromorphone (4,5-α-epoxy-3-hydroxy-17-methyl morphinan-6-one) is a hydrogenated ketone of morphine that is used as a centrally acting opioid analgesic and antitussive. Hydromorphone is a semisynthetic narcotic analgesic prepared from morphine that possesses multiple actions qualitatively similar to those of morphine and is used in medicine as an alternative to morphine. It is mainly used for relief of pain and as a narcotic antitussive for cases of dry, painful coughing. Hydromorphone interacts predominantly with the opioid receptors in the central nervous system (CNS). Its analgesic properties are primarily due to agonist activity at the μ-opioid receptor. Hydromorphone is also a partial agonist of the δ-opioid receptor and an agonist of the κ-opioid receptor. Additionally, hydromorphone exhibits antitussive properties by suppressing the cough reflex in the medullary cough center of the brain.
Patients taking opioid analgesics such as hydromorphone for pain and/or cough relief can become unintentionally addicted. As tolerance to the opioids develops, higher amounts of the drug are needed to alleviate the symptoms and generate the sense of wellbeing initially achieved with the prescribed dose. This leads to dose escalation, which, if left unchecked, can lead rapidly to addiction. In some cases patients have become addicted in as little as thirty days.
Opioid induced constipation (OIC) is a common side effect of pain treatment with opioids. It affects approximately 40-90% of the patients who are chronically taking opioid medication. Additionally, patients suffering from OIC may become resistant to laxative treatments. Although the mechanism is not yet fully understood, it is assumed that the binding of agonists to the peripheral μ-opioid receptors in the gastrointestinal (GI) tract is the primary cause of OIC. This opioid receptor activation impairs the coordination of the GI function by the enteric nervous system (ENS) resulting in decreased gut motility by delaying the transit time of fecal content through interference with the normal tone and contractility of the bowels. While the contractions of the circular muscles are increased causing non-propulsive kneading and churning (stasis) and increased fluid absorption, the longitudinal smooth muscle tone is decreased causing reduced forward peristalsis and additional time for desiccating fecal matter. Furthermore, the anal sphincter tone is increased making defecation more difficult. The clinical presentation of these effects typically manifests itself in symptoms of hard/dry stool, straining, incomplete evacuation, bloating and abdominal distention.